The disclosures herein relate generally to information handling systems (IHS's) and more particularly to reducing undesired impedance discontinuities associated with closely spaced expansion connectors on the bus of such a system.
As the value and use of information continue to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system (IHS) generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user, or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Many IHS's include a main board or motherboard in which several expansion connectors are situated on a common bus, for example a Peripheral Component Interconnect (PCI) bus. Each expansion connector is capable of receiving an expansion card to provide additional capability to the system. The expansion cards are generally mounted perpendicular to the motherboard.
However, as the physical size of many IHS's continues to decrease, it has become increasingly difficult to install expansion cards within the system enclosure. One solution to help alleviate this problem is the so-called “riser card”. A riser card is a card which plugs into a bus connector much like any other expansion card would, namely perpendicular to the motherboard. However, the riser card itself includes one or more bus connectors into which respective expansion cards can be installed. Those expansion cards that are mounted on the riser card will be perpendicular to the riser card and thus parallel to the motherboard. This results in a more compact arrangement.
It has been found that when two expansion bus connectors, such as one on the motherboard and one on the riser card, are spaced very closely together to fit within a 1U enclosure (1 unit or approx 1.75 inches), they together create an significant impedance discontinuity. In other words, the combined impedance of the expansion connectors is significantly higher than the impedance of the bus to which the connectors are connected. This tends to degrade signals traveling across the connections thus formed.
Therefore, what is needed is a method and apparatus for reducing the aggregate impedance discontinuity which occurs when two expansion connectors are located very close to one another on a bus.